Shaft brake assembly

ABSTRACT

A shaft brake assembly for stopping inertial rotation of a drive shaft wherein a brake shaft is secured against rotational movement by means of a disc, the disc being fixedly secured to a housing, the brake shaft being continuously biased to move into contact with the drive shaft, a piston being movable by fluid pressure to remove the brake shaft out of contact with the drive shaft.

United States Patent [191 Hedrick June 26, 1973 [54] SHAFT BRAKEASSEMBLY 3,599,760 8/1971 Moss 188/170 [75] Inventor: John R. Hedrick,La Crescenta,

Calif- Primary Exammer-R1chard E. Aegerter Assistant Examiner-+1. S.Lane [73] Assrgnee: Hall International Inc., Santa Attorney smyth,Roston & Pavia Barbara, Calif.

[22] Filed: Mar. 31, 1971 57 ABSTRACT [21] Appl. No.: 129,766 A shaftbrake assembly for stopping inertial rotation of a drive shaft wherein abrake shaft is secured against [52] US. Cl. 188/70 rotational movementby means of a disc the disc being [51] Int. Cl. Fl6d 65/24 fixedlysecured to a housing the brake Shaft being 58 Field of Search 188/170biased into Contact with the drive shaft, 2. piston being movable byfluid pressure to re- [56] References Cited move the brake shaft out ofcontact with the drive UNITED STATES PATENTS shaft 1,561,722 11/1925Jimerson... 188/170 8 Claims, 3 Drawing Figures PATENTED 2 5 I975 c/OVA/R fiZOP/CX INVENTOR. BY V ki 1M Arrow/5K5 1 SHAFT BRAKE ASSEMBLYBACKGROUND OF THE INVENTION The field of this invention relates to abrake and more particularly to a brake for a shaft which continues toroate due to inertia afer disconnection of the driving power.

Portable tools are in extremely common use. Such a tool usually takesthe form of a hand held drill which includes a motor assembly formedwithin the drill. For example, dentists normally employ the use of suchan apparatus to drill into a persons teeth to permit the insertion of ametallic fitting to eliminate continual tooth decay. Also, in the fieldof medicine, medical doctors frequently use air driven tools. Anexample, of a medical type of air driven tool would be an abrasivewheel, which is either electrically or pneumatically driven, usable bysurgeons for performing skin grafts.

Such tools that are used by doctors and dentists are frequently employedin situations where a high degree of precision is required. For example,a dentist desires to drill into the persons tooth a specific depth butdoes not desire to overdrill. For this reason, when the dentist shutsoff the drilling mechanism, it is desired that the drilling shaft stopinstantly. Similar situations occur in regard to the medical profession.

Also, it is important to effect changing of the tools in a quick mannerin certain instances. For instance, the doctor or dentist may beinvolved in an emergency situation wherein it is not desirable to losetime in the substituting of different tools to the source of pressurizedfluid. For that reason, once the tool is shut off, it is undesirable towait for the tool to quit rotating due to inertia force. Therefore, itis desirable that once the tool is shut down, the tool head immediatelystops rotating.

It would be desirable to design a brake for the drive shaft of arotating tool which was of simple construction yet effected a positivesure brake of the drive shaft when necessary.

SUMMARY OF THE INVENTION The shaft brake of this invention is designedto be incorporated within a drive shaft driven tool assembly. The shaftbrake assembly of this invention is designed to be employed incombination with a pneumatically driven tool wherein the driving fluidpressure is supplied to a piston. The piston is normally biased by aspring assembly in a direction opposite to the fluid pressure. Anextension is secured to the piston which is formed of a non-circularconfiguration such as an eliptical configuration or a polygonalconfiguration. The forward end of the extension is to function as thebraking surface and is adapted, under action of the spring, to come intocontact with the free end of the BRIEF DESCRIPTION OF THE DRAWING FIG. 1is a longitudinal cross sectional view of the brake assembly of thisinvention showing the shaft brake in the braking position;

FIG. 2 is a cross sectional view taken along line 22 of FIG. 1 butshowing the shaft brake in the nonbraking position; and

FIG. 3 is a sectional view taken along line 3-3 of FIG. 1 showing ingreater detail the disc employed within this invention to preventrotational movement of the brake shaft.

DETAILED DESCRIPTION OF THE SHOWN EMBODIMENT Referring particularly tothe drawing there is shown in FIG. 1 a shaft brake assembly 10 of thisinvention including a brake shaft 12 which is to function to be movableinto contact with a tool drive shaft 14. It is to be understood that thetool drive shaft 14 is to be rotated by a motor assembly not shown,such'motor assembly being conventional and forming no specific part ofthis invention. The forward end of the brake shaft is formed, in crosssectional configuration, into flattened sides 16 and 18 with roundedends 20 and 22. It is to be understood that although this particularconfiguration is desirable, this invention is not to be limited thereto.A polygonal configuration such as a square shape or-octagonal shapewould also be satisfactory. However, it is important that theconfiguration of this end of the brake shaft 12 be non-circular.

The brake shaft 12 is integrally secured to a piston 24. Piston 24 islocated within a chamber 26 and capable of axial movement therein.Piston 26 is formed of a substantially hollow interior forming a springretaining chamber 28. A spring 30 is to be located within the chamber 28and is adapted to contact the closed end 32 of the chamber 26.

Fluid under pressure, which would normally be air, is to be suppliedthrough orifice 34 from the main fluid supply passage (not shown). It isto be noted that the fluid is to be supplied at the front end ofchamber- 26 so as to react against the head of the piston 24 and tend tomove the piston 24 against the action of the compression spring 30.

The piston 24 is supported within the housing 38. Housing 38 alsoincludes a shoulder 40 which is adapted to receive a disc 43 located inabutting contact therewith. It is to be noted that the disc 43 iscircular in outer configuration but includes an aperture therein whichis to matingly cooperate with the non-circular configuration of thebrake shaft 12. The disc 43 is to be fixedly retained with respect tothe housing by means of snap ring 44. It is to be further noted that thebrake shaft 12 is capable of longitudinal movement with respect to thedisc 43. However, because of the noncircular mating aperture of the disc43, rotational movement of the brake shaft 12 with respect to the disc43 is prevented.

It is desired that the disc 43 be constructed of a particular type ofplastic material commonly referred to bythe trade name of Teflon. Such adisc permits low frictional movement of the shaft 12 with respect to thedisc 43. Also, such a disc functions to damp vibrations which may occurduring the braking procedure. It is common for the shaft to rotate at avelocity of 100,000 rpm. To brake from such a velocity quickly, normallycauses rapid transverse movement of the shaft 12. This transversemovement can cause premature failure of certain parts as well asexhibiting a most undesirable noise. The plastic disc 43 effectivelydamps these vibrations and eliminate the noise associated therewith.

Additionally, a predetermined amount of space exists between the shaft12 and the disc 43. This space is to permit conducting of thepressurized fluid from chamber 26 to drive the motor assembly (notshown).

The operation of the shaft brake assembly of this invention is asfollows: It will be presumed that the shaft brake assembly of thisinvention is in the non'braking position shown in FIG. 2 of the drawing.in that position fluid pressure within the fluid supply passage istransmitted through orifice 34 into chamber 26 and reacts against piston24. As a result, piston 24 is moved within chamber 26 to compress spring30 and to displace the brake shaft 12 from the drive shaft 14. In thisposition the drive shaft 14 is free to rotate in an unhindered manner.

Let it be assumed that the operator shuts off the supply of pressurizedgas which drives motor assembly driving the drive shaft. The gaseousfluid under pressure is no longer being supplied within chamber 26,permitting the biasing force caused by spring 30 to move the piston 24toward the front end of chamber I 26. As a result, the brake shaft 12 ismoved into contactual relationship with the driveshaft 14. Spring alsoprovides sufficient force to provide sufficient frictional resistance ofthe brake shaft when coming into contact with the drive shaft 14.Rotation of the brake shaft 12 with respect to the housing 38 isprevented by means of disc 43. Disc 43 is fixedly secured to the housing38 by means of snap ring 44. Formed within the disc 43 is a non-circularaperture which cooperates with the noncircular configuration of thebrake shaft 12, thereby preventing rotation of the brake shaft 12 withrespect to the housing 38.

What is claimed is: 1. An assembly to brake a fluid motor driven driveshaft against rotation thereof comprising:

a housing in which said drive shaft is rotatably mounted, a brake shaftfixedly mounted in said housing, means for biasing said brake shaft intofrictional engagement with said drive shaft to exert a braking action onsaid drive shaft, fluid actuated means for biasing said brake shaft awayfrom frictional contact with said drive shaft, meansfor transferringfluid from said fluid actuated means to the motor which drives saiddrive shaft,

means fixedly secured to said housing and operatively associated withsaid brake shaft for preventing rotation of said brake shaft withrespect to said housing,

said last mentioned means including a disc, said disc having anoncircular aperture therein, said brake shaft extending through saidaperture, that portion of said brake shaft extending through saidaperture having at least a partially complementary periphery thereon,

a space within said aperture located between the periphery of said brakeshaft and the rim of the aperture of said disc, said space comprising atleast a portion of said transferring means, and

said disc being formed of a plastic material exhibiting low frictionalcharacteristics to movement between said disc and said brake shaft todamp vibration of said shaft.

2. An apparatus for braking a fluid operated motor comprising:

means defining a chamber having an inlet for admitting fluid underpressure to said chamber and an outlet for exhausting fluid from saidchamber whereby fluid can flow through said chamber from said inlet tosaid outlet,

means for conducting the fluid from said outlet to the fluid operatedmotor to drive said motor,

a rotatable element rotatable by the fluid operated motor,

a brake member,

means for mounting the brake member for movement into and out ofengagement with the rotatable element,

means for biasing the brake member into engagement with said rotatableelement, and

means responsive to the fluid in said chamber being of at least apredetermined pressure for holding said brake member substantially outof contact with said rotatable element.

3. An apparatus for braking a fluid operated motor comprising:

means defining a chamber,

conducting means connectible to a source of fluid under pressure and tothe fluid operated motor for conducting fluid under pressure from saidsource through at least a portion of said chamber to the motor to drivethe motor,

a brake member,

a rotatable member rotatable by the fluid operated motor,

means for mounting one of said members for movement into and out ofengagement with the other of said members,

yieldable means for urging said one member into braking contact with theother of said members to cause a braking force to be applied to saidrotatable member, and

a fluid responsive member at least partially in said chamber andresponsive to the pressure in said chamber being at least apredetermined magnitude for urging said one member out of brakingcontact with said other member.

4. An apparatus for braking a fluid operated motor comprising:

a housing,

a rotatable element,

means in said housing for mounting said rotatable element for rotationby the motor, I

a brake member,

a piston coupled to said brake member,

means in said housing defining a chamber,

said piston and brake member being atleast partially mounted in saidchamber for movement together, said brake member being movable generallyaxially into and out of braking contact with the rotatable element,

means for substantially preventing rotation of said conducting meansconnectible to a source of fluid under pressure and to the fluidoperated motor for conducting fluid under pressure to the fluid operatedmotor to drive the motor,

a rotatable element rotatable by the fluid operated motor,

a brake member,

means for mounting said brake member for movement into and out ofengagement with said rotatable element,

yieldable means for urging the brakemember into contact wtih therotatable element to apply a braking force thereto,

a fluid responsive member responsive to a predetermined condition of thefluid in the conducting means for urging said brake member out ofcontact with said rotatable element, and at least a portion of at leastone of one of said members being positionable in said conducting means.

6. An apparatus as defined in claim 5 wherein at least member extends,the aperture and the cross section of said brake member being configuredto prevent rotation of the brake member. I

8. An apparatus as defined in claim 7 wherein said aperture definingmeans includes a disc, the clearance between the rim of the aperture andthe brake member forming a portion of said conducting means.

i It

1. An assembly to brake a fluid motor driven drive shaft againstrotation thereof comprising: a housing in which said drive shaft isrotatably mounted, a brake shaft fixedly mounted in said housing, meansfor biasing said brake shaft into frictional engagement with said driveshaft to exert a braking action on said drive shaft, fluid actuatedmeans for biasing said brake shaft away from frictional contact withsaid drive shaft, means for transferring fluid from said fluid actuatedmeans to the motor which drives said drive shaft, means fixedly securedto said housing and operatively associated with said brake shaft forpreventing rotation of said brake shaft with respect to said housing,said last mentioned means including a disc, said disc having anoncircular aperture therein, said brake shaft extending through saidaperture, that portion of said brake shaft extending through saidaperture having at least a partially complementary periphery thereon, aspace within said aperture located between the periphery of said brakeshaft and the rim of the aperture of said disc, said space comprising atleast a portion of said transferring means, and said disc being formedof a plastic material exhibiting low frictional characteristics tomovement between said disc and said brake shaft to damp vibration ofsaid shaft.
 2. An apparatus for braking a fluid operated motorcomprising: means defining a chamber having an inlet for admitting fluidunder pressure to said chamber and an outlet for exhausting fluid fromsaid chamber whereby fluid can flow through said chamber from said inletto said outlet, means for conducting the fluid from said outlet to thefluid operated motor to drive said motor, a rotatable element rotatableby the fluid operated motor, a brake member, means for mounting thebrake member for movement into and out of engagement with the rotatableelement, means for biasing the brake member into engagement with saidrotatable element, and means responsive to the fluid in said chamberbeing of at least a predetermined pressure for holding said brake membersubstantially out of contact with said rotatable element.
 3. Anapparatus for braking a fluid operated motor comprising: means defininga chamber, conducting means connectible to a source of fluid underpressure and to the fluid operated motor for conducting fluid underpressure from said source through at least a portion of said chamber tothe motor to drive the motor, a brake member, a rotatable memberrotatable by the fluid operated motor, means for mounting one of saidmembers for movement into and out of engagement with the other of saidmembers, yieldable means for urging said one member into braking contactwith the other of said members to cause a braking force to be applied tosaid rotatable member, and a fluid responsive member at least partiallyin said chamber and responsive to the pressure in said chamber being atleast a predetermined magnitude for urging said one member out ofbraking contact with said other member.
 4. An apparatus for braking afluid operated motor comprising: a housing, a rotatable element, meansin said housing for mounting said rotatable element for rotation by themotor, a brake member, a piston coupled to said brake member, means insaid housing defining a chamber, said piston and brake member being atleast partially mounted in said chamber for movement together, saidbrake member being movable generally axially into and out of brakingcontact with the rotatable element, means for substantially preventingrotation of said brake member, biasing means in said housing, andconducting means connectible to a source of fluid under pressure and tothe fluid operated motor for conducting fluid under pressure through atleast a portion of said chamber to the motor to drive the motor.
 5. Anapparatus for braking a fluid operated motor comprising: conductingmeans connectible to a source of fluid under pressure and to the fluidoperated motor for conducting fluid under pressure to the fluid operatedmotor to drive the motor, a rotatable element rotatable by the fluidoperated motor, a brake member, means for mounting said brake member formovement into and out of engagement with said rotatable element,yieldable means for urging the brake member into contact wtih therotatable element to apply a braking force thereto, a fluid responsivemember responsive to a predetermined condition of the fluid in theconducting means for urging said brake member out of contact with saidrotatable element, and at least a portion of at least one of one of saidmembers being positionable in said conducting means.
 6. An apparatus asdefined in claim 5 wherein at least a portion of said brake element ispositioned in said conducting means.
 7. An apparatus as defined in claim5 including means defining an aperture through which the brake memberextends, the aperture and the cross section of said brake member beingconfigured to prevent rotation of the brake member.
 8. An apparatus asdefined in claim 7 wherein said aperture defining means includes a disc,the clearance between the rim of the aperture and the brake memberforming a portion of said conducting means.